Nonwoven fabrics and methods of making the same



June 30, 1970" A. H. BRELI' CH 'NONWOVENFABRICS AND METHODS 01" MAKING 'rm-z -Mum:

Originai Filed March 9, 1902 mvsw'rom Jen/ax A 0254/0.

A TQRNEL United States Patent 01 3,518,041 Patented June 30, 1970 ice ABSTRACT OF THE DISCLOSURE A non-woven bonded textile fabric rendered durable in the presence of .water by bonding with polyvinyl alcohol and cross-linking said polyvinyl alchol binder in situ with a formaldehyde crosslinking agent.

This is a continuation of application Ser. No. 178,604,

filed Mar. 9, 1962, now abandoned.

Most present day nonwoven fabrics are made from cel- 2 Claims 9 lulose fibers laid down in a web or layer of overlapping,

intersecting fibers with a bonding agent applied to form a self-sustaining fabric. Many different bonding agents are used for this purpose, among which is polyvinyl alcohol.

Polyvinyl alcohol makes an excellent binder for cellulose fiber webs; however, its water-solubility has militated.

against its widespread use to bind the overlapping and intersecting fibers in a web because the resulting nonwoven fabric did not have the desired durability.

Many attempts have been made to render polyvinyl alcohol Water-insoluble so as to overcome the noted objection to its use as a binder for nonwoven fabrics; for example, through the use of formaldehyde cross-linking agents to cross-link hydroxyl groups of the polyvinyl alcohol. Only partial success has been achieved through this avenue because the formaldehyde cross-linking agents tend to embrittle the fibers of the fabric and thereby reduce its strength. Further, the formaldehyde cross-linking agents often cross-link the cellulosic fibers of the base web and thus reduce softness and absorbability;

The present invention contemplates a nonwoven fabric comprising cellulosic fibers and a polyvinyl alcohol resin binder either in film, powder, fiber, or other particulate form, which is cross-linked in situ with a formaldehyde cross-linking agent to insolubilize the binder. The amount of formaldehyde used to insolubilize the polyvinyl alco hol resins in accordance with the present invention is controlled to provide in the finished fabric a content of formaldehyde varying from about 0.1% to 0.8%, preferably about 0.15% to 0.6%, based on the weight of the fabric,

substantially all of which is bound to or cross-linked with, the polyvinyl alcohol. The fabric of this invention is substantially free of unbound formaldehyde and there is no cross-linking-or substantially no cross-linkingof formaldehyde with the cellulosic fibers. In consequence the resulting fabric is strong and durable and maintains its desired absorbent properties. I

The cellulosic fibers which may be used to form the starting base webs of this invention may be either natural or artificial fibers such as cotton, manila hemp, viscose rayon,

cuproammonium rayon, etc. The cellulosic fibers may be used alone or in combination with other natural or synthetic fibers such as wool, nylon, polyesters, i.e., Dacronf etc.

The base webs may be formed by any of the techniques well-known in the art, such as carding, air-laying, waterdepositing, etc. These base webs or fibrous layers may be used as single units for lightweight fabrics or they may be plied with themselves as desired to produce heavier weight fabrics.

The base web in single layer or laminate form, is bonded with polyvinyl alcohol in accordance with conventional procedures. Thus, for example, a solution of polyvinyl alcohol may be applied to the web either over all or in a ,predetermined pattern of spaced binder areas, and the web dried by heating. Alternatively, the polyvinylalcohol may be applied in the form of polyvinyl alchol fibers added to the fibers of the web as a preliminary to its formation. This web is treated with water as by immersion, for example, to soften the polyvinyl alcohol fibers and the web is dried by heating.

The polyvinyl alcohol used will have a specific gravity of about 1.19 to 1.29. It is a straight chain compound or a predominantly straight chain compound soluable in hot water but diificultly soluble or insoluble in cold water.

The polyvinyl alcohols employed within the principles of the present invention have a percent hydrolysis of at least about 8.7% and preferably a percent hydrolysis of 98% or more. Examples of polyvinyl alcohols suitable for use in accordance with the invention are the commercially available polyvinyl alcohol compounds sold under the trade names Elvanol, Gelvatol, Polybond, Resyn, etc.

The polyvinyl alcohol may be applied to the fibrous web by passing or saturating the base web with an aqueous solution of the polyvinyl alcohol resin, or as previously mentioned, by incorporating polyvinyl alcohol fibers in the base web and passing this web through water to activate the polyvinyl alcohol. In all instances from about 1% to 50%, preferably from about 1% to 10%, of polyvinyl alcohol based on the weight of the final fabric may be employed in forming the fabrics of this invention.

The finished fabric of this invention will weigh fromabout 100 grains per square yard to about 4,000 grains per square yard, though it is preferred that the weight of the finished fabric be from about grains per square yard to about 2,000 grains per square yard.

In carrying out the present invention, the base web of cellulosic fibers and the polyvinyl alcohol are contacted with water containing a small amount of a formaldehyde cross-linking agent and a controlled amount of catalyst to accelerate the cross-linking. The treated base web is heated to drive off the water and effect the desired crosslinking of alcohol and formaldehyde, thereby forming the durable nonwoven fabric of the invention.

The cross-linking reaction may be carried out under conditions known in the art, such as exposure for 2 minutes in air at 350 F. In accordance with the invention the conditions for effecting cross-linking need not be a stringent as is conventional in the prior art. For example, the cross-linking may be effected by subjecting the web carrying the reactants to temperatures of about 300 F. for as little as about one-half minute or somewhat less. Times for the reaction of up to about 5 minutes are not detrimental to the product.

The formaldehyde cross-linking agents suitable for use in this invention are elementary formaldehyde, paraformaldehyde and other compounds which decompose to liberate formaldehyde, i.e., to engender formaldehyde or resins, usually nitrogenous, which contain formaldehyde in reactive form. Particularly preferred for this purpose 3. I 7 are water-soluble precondensates such as methylol urea, methylol melamine andthe like.

Many substances are known to catalyze the reaction of formaldehyde and polyvinyl alcohol and these may be used in accordance with the invention. In general these are acidic substances such as common mineral acids or substances which become acidic at the elevated temperatures at which the reaction takes place, for example, tartaric acid, lactic acid, boric acid, various sulfonic acids, oxalic acid, acetic acid, formic acid, salts such as ammonium thiocyanate, ammonium acid phosphate, ammonium chloride and the like. p

The concentration of formaldehyde in the finished fabric willlie within the range of from about 0.1% to about 0.8% by weight depending on the structure and composition of the fabric, the finish desired, and other considerations. The preferred concentration of formalde adjacent cellulosic fibers and bond them together. On

2 continued heating the water is driven off and the desired hyde in the finished fabric is from about 0.15% to about 0.6%. At formaldehyde contents substantially below the indicated range the'insolubilizing action is insufficient for practical benefit. As the formaldehyde content in the fabric is raised above the indicated range there is very little if any increase in the strength and, if too much formaldehyde is used, the fabric becomes embrittled and loses strength. Furthermore, at these higher levels of formaldehyde concentration the cellulosic fibers are crosslinked and the fabric loses absorbency. The catalyst concentration is important in controlling the desired concentration of formaldehyde in the finished fabric. The concentration of catalyst depends on the acid strength of the catalyst material used and, in general, should not be greater than the amount which would lower the pH of the final fabric about 0.5 unit. It is preferred that the catalyst concentration be such that it does not measurably lower the fabric pH.

When the catalyst for formaldehyde cross-linking is sulfuric acid the optimum concentration is about 0.05% (N/ 100), assuming 100% liquid pickup of the water solution. At this solution pickup the range of the sulfuric acid catalyst is from about 0.025% to about 0.1% (N/200 to N/50). This normality range is higher than that desired for strong acid catalysts such as hydrochloric acid; but lower than can be used for weak acids or acid salts, or materials which decompose on heating with acid reaction, such as magnesium chloride, ammonium thiocyanate, lactic acid and the like. Concentrations of 0.5% by weight may be used when the latter catalysts are employed. If the concentration of catalyst is raised above the indicated range the fabric is embrittled, and if the concentration of catalyst is less than the indicated range the process will be inefficient and wasteful as there will be considerable unbound formaldehyde present in the operation.

The formation of the fabrics of the present invention will be more fully described in conjunction with the drawing which is a diagrammatic representation showing an illustrative arrangement of equipment by means of which the invention may be carried out continuousy.

Referring to the drawings, base webs and 11 of cellulosic fibers and polyvinyl alcohol fibers, produced, for example, by the carding engines 12 and 13, are plied together by placing one on top of another on an advancing conveyor 14 which conveys the plied webs to a wetout mangle comprising a trough 15 containing water, formaldehyde cross-linking agent and catalyst. A rotating roll 16 picks up the solution from the trough and applies it to the web as the same passes between this roll and a back-up roll 17. The impregnated web passes to a series of dry cans 18 which are heated to drive off the water and react the formaldehyde cross-linking agent and the polyvinyl alcohol. The dried web" is then passed to a wind-up roll 19 for immediate use or for delivery to storage.

During-the initial heating of the impregnated fabric on cans 18 the water in the fabric is'heated and it softens the polyvinyl alcohol fibers and causes them to adhere to insolubilizing reaction takes place.

The invention will be further illustrated by the following examples. The percentages indicated are by weight unless specifically stated otherwise.

EXAMPLE 1 Three card webs, each weighing approximately 200 grains per square yard and containing 97 /2% viscose rayon fiber, 1 /2 denier, 1%; inches in length, and 2 /2% polyvinyl alcohol'fiber, 1.4 denier, 1% inches in length, are plied together to form a base web. The polyvinyl alcohol fiber used is the hot water-soluble, non-acetylized and not heat treated species. sold by Kurashiki Rayon Company, Ltd. under the trade name Vinylon.

The base web is impregnated in a mangle with a water solution containing .25% of an essentially monomeric methylol melamine cross-linking agent (sold by American Cyanamid Company under the trademark Aerotex'UM) and N/200 sulfuric acid. Solution pickup from the bath is about 200% by weight of the starting web. The fabric is then dried at a temperature of about 220 F. and heated in an over for 2 minutes at 350 F. The bound formaldehyde content of the fabric is 0,26% occurring principally in the polyvinyl alcohol fiber as determined by means of conventional chemical staining tests. The treated fabric absorbs cold water readily.

A sample of the final fabric is boiled in water for approximately 2 minutes with no apparent effect. At the same time another sample of the base web treated in a similar manner with the exception that the formaldehyde cross-lnking agent and the catalyst were omitted from the 'mangling step was boiled in water and fell apart immediately in the boiling water.

EXAMPLE 2 A card web weighing approximately 600 grains per square yard and containing viscose rayon fiber, 1% denier, 1%; inches in length, and 10% polyvinyl alcohol fiber, nonactylized, not heat treated, hot water-soluble, 1.4 denier and 1% inches in length, is passed through a mangle and impregnated to approximately 200% pickup with a formaldehyde cross-linking water solution containing approximately 1.0% of Aerotex UM and N/ 100 sulfuric acid as a catalyst. The impregnated fabric is passed over a series of dry cans at a temperature of approximately 300 F. to drive off the water and cross-link the polyvinyl alcohol fibers. The bound formaldehyde content is 0.78%. The treated fabric absorbs cold water readily.

The fabric was boiled in water for approximately 2 minutes with no deleterious effect. A piece of this fabric was stained with osmic acid and showed that only the polyvinyl alcohol fiber was cross-linked and that the viscose rayon fiber was unaffected.

In a comparative test the methylol melamine is applied from a 2% solution. Catalyst concentration is maintained at N/ 100 sulfuric acid. Bound formaldehyde is 1.40%. The fabric has poor absorbency.

EXAMPLE 3 The procedure of Example 1 is repeated except that the cross-linking agent is substituted methylol triazone sold by Dan River under the trade name Stanset Z98. The bound formaldehyde content of the fabric is 0.23%. The fabric treated as in the previous examples gives similar results. i EXAMPLE 4 The procedure of Example 1 is followed except that the base fabric to which the cross-linking agent is applied contains 97 /2 cotton fiber and a 2 /2 polyvinyl alcohol fiber. The fabric tested as in the previous examples gives similar results.

EXAMPLE 5 An all rayon card web weighing approximately 600 grains per square yard of viscose rayon fibers, 1V2 denier, 1 inches in length is impregnated in a mangle with an aqueous solution containing approximately 2 /2% polyvinyl alcohol resin, 0.5% Aerotex UM and 'N/,200 sulfuric acid. The polyvinyl alcohol has a percent hydrolysis of at least 99 and a corresponding saponi-fication number of less than 12.6, a viscosity of about 60 centiposes and a pH of 6-8. Solution pickup is about 200% based on the weight of the base web. The impregnated fabric'is passed over dry cans at a temperature of approximately 300 F.

to drive off the water and cross-link the polyvinyl alcohol resin. The bound formaldehyde content of the fabric is 0.27% occurring principally in the polyvinyl alcohol resin as determined by convention chemical staining tests. The treated fabric absorbs cold water readily. A sample of the final fabric is boiled in water for approximately two minutes with no deleterious effects.

EXAMPLE 6 The procedure of Example 5 is followed except that the acid catalyst used is magnesium chloride at /2 concentration in the impregnating solution. The fabric tested as in previous examples gives similar results.

Although several specific examples of the inventive concept have been described, the same should not be construed as limited thereby nor to the specific features mentioned therein but to include various other equivalent features as set forth in the claims appended hereto. It is understood that any suitable changes, modifications and variations may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. An absorbent nonwoven textile fabric having textilelike softness, drape and hand comprising a web of overlapping, intersecting cellulosic fibers bonded with from about 1% to about 50% by weight of a non-acetylized polyvinyl alcohol binder in fiber form and having a percent hydrolysis of at least about 87%, said fibers of polyvinyl alcohol binder being cross-linked in situ and having a bound formaldehyde concentration in the finished fabric of from about 0.1% to about 0.8% by weight, based on the total weight of the fabric, there being substantially no unbound formaldehyde in said finished fabric, nor any substantial cross-linking of the cellulosic fibers by the formaldehyde; said cross-linking of the polyvinyl alcohol binder fibers being accomplished by formaldehyde in the presence of an acid catalyst which is present in an amount not greater than the amount which would lower the pH of the final fabric by about 0.5 unit, whereby the initial absorbency and textile-like softness, drape and hand of the fabric is maintained and the polyvinyl alcohol binder is provided with water insolubility.

2. A process for producing an absorbent nonwoven textile fabric having textile-like softness, drape and hand which comprises:

(a) forming a web of overlapping, intersecting cellulosic fibers;

(b) incorporating in said web from about 1% to about 50% by weight of a. non-acetylized polyvinyl alcohol binder in fiber form and having a percent hydrolysis of at least about 87%;

(c) impregnating said web with an aqueous solution of a formaldehyde cross-linking agent containing an acid cross-linking catalyst, said formaldehyde crosslinking agent being present in an amount suflicient to cross-link said polyvinyl alcohol binder fibers to provide from about 0.1% to 0.8% bound formaldehyde therein in the finished fabric, said acid catalyst being present in an amount not greater than the amount which would lower the pH of the final fabric by about 0.5 units; and

(d) heating said impregnated web to cause said polyvinyl alcohol binder fibers to soften and adhere to adjacent cellulosic fibers to bond them together and to substantially simultaneously cause said formaldehyde to cross-link said polyvinyl alcohol binder fibers to render the same water-insoluble, there being substantially no unbound formaldehyde in the finished fabric, nor any substantial cross-linking of the cellulosic fibers by the formaldehyde, whereby the initial absorbency and textile-like softness, drape and hand of the fabric is maintained and the polyvinyl alcohol binder is provided with water insolubility.

References Cited UNITED STATES PATENTS 2,452,152 10/1948 Rooney et al. l17-138.8 X 2,880,111 3/1959 Drelich et a1 117140 X 2,940,863 6/ 19-60 Bennett et a1 117-140 X 2,962,762 12/1960 Hartmann et a1. 156-83 X 3,253,715 5/1966 Painter et al 117-140 X HERBERT B. GUYNN, Primary Examiner U.S. Cl. X-IR. 

